Spring probe blocks are used to provide temporary spring contact interfaces between integrated circuits or other electronic equipment and an automated test equipment test head. The automated test equipment performs necessary tests of the integrated circuits or other electronic equipment.
Spring probe block assemblies of the type used in automatic test equipment are widely available and use generally similar designs. Spring probe block housings are typically machined from metal bar stock in an elaborate and costly sequence of processes that assure precise locations and diameters of the bores that accept press-fitted electrical probes and ground receptacles. The solid metal fabrication also serves to commonly ground all of the circuit elements, which is a desirable feature in many applications. Where common grounding of the circuits is not required or desired, it is known that spring probe block housings may also be made of a molded polymer instead of a machined metal. A molded polymer housing provides a significant cost savings versus a machined metal housing. In addition, a housing formed of a conductive polymer material could be used in place of a metal housing to provide a common ground.
With both the metal and polymer probe block housings, coaxial probe connectors are individually terminated to coaxial cables at one end and to spring probes at the other. Typically, one spring probe is provided for each signal line, and one or more spring probes are provided to serve as a reference (i.e., ground) for each signal line. In the case of polymer spring probe housings, coaxial shield tubes and ground spring probes associated with each signal line can be electrically isolated from their neighbors by the dielectric material of the polymer housing. The electrical isolation of each channel (consisting of a signal line plus its associated ground return loop) may be used to achieve higher bandwidths to test faster integrated circuits and also to test integrated circuits more quickly. For example, in commonly assigned patent application Ser. No. 09/804,762, filed Mar. 12, 2001 and titled “High Bandwidth Probe Assembly”, an insulative polymer housing electrically isolates each signal line and associated ground probe from other signal lines and ground probes.
In some instances, it is desired that a portion of the plurality of electrical probes in the housing be electrically isolated, while another portion of the plurality of electrical probes are commonly grounded. For example spring probes used to provide power must be isolated from other grounded probes. Currently, such a device is constructed by using a metal housing or ground plate to provide a common ground for the probes, and then isolating selected probes from the common ground using electrically insulative inserts or sleeves around the selected probes. Although generally effective, such a spring probe block construction is expensive and time consuming to produce. As noted above, the processes required to machine a metal housing is elaborate and costly. Further, the large number of small components (e.g., receptacles, insulator sleeves, etc.) used in such a device adds to the complexity and expense of manufacturing and assembling the device.
In addition to increasing the complexity of the device, the use of receptacles and insulators decreases the spring probe pointing accuracy by adding to the assembly stacking tolerances. Spring probe pointing accuracy is important along the Z-axis (the direction of spring probe movement) as well as along the lateral X and Y axes. Close control of Z axis assembly tolerances is necessary so that a device under test board can be brought very close to the probe block without contacting it. The smallest gap that can be safely achieved is desired to minimize the loop inductance which is proportional to the exposed probe length. Close control of X and Y axis assembly tolerances is necessary to ensure that the probes do in fact make contact with the intended areas of the device under test board. As devices become smaller, stacking tolerances have a greater importance in the pointing accuracy of the device.
Clearly, what is needed is a spring probe block assembly that can provide a cost effective approach for providing both electrically commoned and electrically isolated probes in the probe block. Preferably, such a spring probe block assembly would reduce the number of components used in the completed assembly. Preferably, the spring probe block assembly would also facilitate the replacement of spring probes and coaxial connectors within the probe block assembly without requiring extensive rework or even scrapping of the entire spring probe block assembly. In addition, the spring probe block assembly would preferably be resistant to high cable pullout forces that could inadvertently dislodge the coaxial connectors during motion of the automated test equipment.